Recently, owing to the tendency of the electric and electronic components and sets to be small and thin, IC and LSI packages have been rapidly varied. Particularly, in spite of the fact that the size of chip has become larger, the package has to become thin and small and has high pin numbers. The mounting technology has also varied with surface mounting technology. Recently, a Thin Small Out-line J-Bend Package (TSOJ), having about 1 mm of thickness, is being produced. TSOJ, which is a medium stage type between Small Out-line J-Bend Package (SOJ)/Quad Flat Package (QFP) and Tape Automated Bonding(TAB), will be used as a main type in the memory element field in the near future. According to the change of such a package, resin compositions for sealing semiconductor elements also concurrently requires strict low stress, high heat resistance and high moisture resistance over the prior art compositions.
A method for decreasing inner stress by adding plasticizers such as a modified silicone oil or CTBN(Japanese Laid-open Patent Publication Nos. (Sho) 63-230725; 62-7719; 62-106920; and 62-260817) and a method for lowering thermal expansion coefficient by increasing the amounts of fillers [Advances in Polymer Science 88, 1-48(1989)] are known as low stress techniques. However, such methods have serious problems such as lower heat resistance, moldability and abrasion of equipment.
Meanwhile, Although a method for improving heat resistance by using polyfunctional epoxy resins (Japanese Laid-open Patent Publication Nos. (Sho) 62-477 and 62-7719 and a method for improving heat resistance by using bismaleimide (Japanese Laid-open Patent Publication Nos. (Sho) 62-132961; 62-7723; 54-142298; and 58-215452) are well known, these methods have problems in that due to an increase of the glass transition temperature the moisture resistant property decreases. In addition, it has been suggested that maleimide be added to improve heat resistance (Japanese Laid-open Patent Publication Nos. (Sho) 62-53324 and 62-270618). It has been attempted to increase the thermal property of resin compositions by curing epoxy resins with reaction initiators having functional groups such as COOH, OH, NH, etc. at the terminal of imide backbone. However, there is an upper limit to the amount of imide which contributes to the improvement of the heat resistance property. Japanese Patent Publication Nos. (Sho) 58-215452; 58-89619; 59-64660; 59-227924; 62-227917; etc. disclose a method for reacting an amino group with an epoxy group in resin compositions, by initially reacting compounds having amino groups at the terminal position, for example, p- or m-aminophenol and diaminodiphenylmethane with a commercially available maleimide to obtain a prepolymer, and then adding it to resin compositions. However, this method has difficulties in controlling the degree of reaction and also has a limit in increasing the imide content. A method for increasing the heat resistant property by blending epoxy resins and amine compounds with polyfunctional polymaleimide to improve the curing property is also known. This method also has problems in storage stability at room temperature (20.degree. to 30.degree. C.) and difficulties in homogeneous curing reactions. Japanese Laid-open Patent Publication Nos. (Sho) 59-227918; 62-268132; 63-230728; etc., disclose modified curing agents, which are curing agents for epoxy resins and capable of reacting with both epoxy and maleimide by incorporating an allyl group into phenolnovolak resins, and curing agents having both hydroxy groups and allyl groups in the epoxy resins. Since the latter is prepared by incorporating an allyl group into phenol resins and then reacting the resulting product with epoxy resins, it is a complex and costly process.
Therefore, the object of the present invention is to provide novel imide-epoxy resins, wherein an epoxy group is incorporated into a bismaleimide which is useful for improving heat resistance to resin compositions and a process for preparing the same.
Another object of the present invention is to provide resin compositions in which an epoxy group is incorporated into a maleimide to impart low stress properties and high moisture and heat resistance for sealing super thin high integrated IC elements.